In metal connection in electrical and electronic devices or the like, solder connection using a solder paste has been generally used and in such a solder paste, a solder alloy containing lead has been conventionally used.
However, in view of environmental load, the use of lead has been recently required to be suppressed and thus, the development of a solder alloy without containing lead (lead-free solder alloy) has been promoted.
As such a lead-free solder alloy, for example, a tin-copper alloy, a tin-silver-copper alloy, a tin-bismuth alloy, and a tin-zinc alloy have been well known and among all, a tin-silver-copper alloy has been widely used for its excellent strength.
As such a tin-silver-copper solder alloy, for example, a solder alloy containing silver at a ratio of 2 to 4 mass %, copper at a ratio of 0.1 to 1 mass %, bismuth at a ratio of 0.5 to 4.8 mass %, nickel at a ratio of 0.01 to 0.15 mass %, cobalt at a ratio of 0.001 to 0.008 mass %, furthermore, indium at a ratio of 2.2 to 6.2 mass %, and tin as a remaining content has been proposed (ref: Patent Document 1).
Such a solder alloy has a low melting point; has excellent mechanical properties such as durability, crack resistance, and erosion resistance; and furthermore, is capable of suppressing the occurrence of a void (gap).